Eatable shellfish such as lobsters and crabs, consist primarily of water and meat. The ratio MC is the ratio of meat to water plus meat by weight. When the MC of a lobster or crab is at least about 19%, this indicates that the lobster or crab is ready for harvesting. That is, that the lobster or crab can be shipped to a market for later human consumption. When the MC is no more than about 7%, this indicates that the lobster or crab is not in a condition for shipment to a market. In most cases, such a low percent of meat is due to the animal having just completed molting (recently having shed its shell and grown a larger shell) or being diseased. When the shellfish are being raised in seafood farming, it is generally desirable to release the animal, so a molting animal can recover and a diseased animal can recover or die. Although lobsters, crabs, and other shellfish often can be correctly evaluated by color, weight, and other characteristics by an experienced shellfish handler, it would be desirable if a more accurate and/or objective evaluation of a shellfish could be obtained, and if this could be done by a less experienced person.
The prior art suggests the use of the velocity of sound through large farm or ranch animals such as cattle and sheep, to determine the amount of fat in the animal, and it has been speculated that such velocity measurements might be useful for a wide range of animals. However, the structure of shellfish is very different from that of cattle and sheep. That is, for shellfish, a major question is whether the animal should be harvested or put back, based upon the percent of meat to total body mass which is substantially equal to meat plus water.
When sonic energy is transmitted through a cow or sheep, this can be done by pressing the faces of transducer devices against a pinched portion of the animal with sufficient force to assure that the transducer faces make wide area contact with the animal. However, with a shellfish, the shell is rigid and the face of the transducer device cannot be made to assure contact with a wide area of most shellfish. A large force against the shell will crack it, resulting in the early death of a shellfish. A method and apparatus for readily determining the meat ratio, or MC, in a live shellfish without injuring the shellfish, would be of value.
In accordance with one embodiment of the present invention, a method and apparatus are provided for detecting MC, which is the ratio of meat to meat plus water in a shellfish, especially in a lobster or crab. This is accomplished by pressing a pair of transducer devices against opposite locations of the shell of the shellfish, without substantially deforming or cracking the shell, and measuring the velocity of sound between those locations. A sound-carrying flowable material, especially a gel, is preferably applied to lie between the face of each transducer device and a corresponding location on the shellfish, to provide good acoustic coupling without excessive pressure that would crack the shell of the shellfish.
Shortly (the same day) before the faces of the transducer devices are pressed against locations on the shellfish, the apparatus is calibrated to determine the velocity of sound between the faces. This enables calibration of the apparatus for particular parameters including temperature and the present state of the electronic circuitry. After the period of time required for sound to pass between the transducers is determined for zero spacing of the faces, the faces of the transducer devices are moved apart and then pressed against opposite locations on the shellfish and a measurement is taken.
At least xc2xeths of the time, a shellfish is harvested for transport to market and human consumption when the velocity of sound through the shellfish is at least 1660 m/sec. At least xc2xeths of the time, the shellfish is not harvested for transport and human consumption when the velocity of sound through the shellfish is less than 1560 m/sec. A velocity of 1660 m/sec. has been determined to indicate 19% meat ratio, while a velocity of 1560 m/sec. indicates 7% meat ratio, for both a lobster and a crab. A velocity of about 1600 m/sec, which indicates a 12% meat ratio is a borderline between harvesting or not.
A horn lies between each transducer and the shell of a shellfish, to provide a time delay so the entire pulse can leave the transducer before reflected energy reaches the transmitting transducer.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.